This application relates to a fire protection method and system for the protection of residential occupancies having ceilings with a pitch up to 12/12.
Fire protection sprinklers conventionally are connected to a conduit to receive pressurized fire-extinguishing fluid, such as water. Fire protection sprinklers may be mounted on a fluid conduit running along a ceiling and may either depend downward from the conduit, which is referred to as a “pendent” configuration, or may extend upward, which is referred to as an “upright” configuration.
Residential construction often includes a variety of ceiling configurations, including curved, horizontal, beamed, and sloped ceilings such as those commonly known as “cathedral” ceilings. NFPA 13, Chapter 3, defines a “sloped ceiling” as a ceiling with a slope exceeding 2 in 12, a “flat ceiling” as a continuous ceiling in a single plane, and a “horizontal ceiling” as a ceiling with a slope not exceeding 2 in 12. (NFPA 13, 2007 Edition, 3.3.4.) Moreover, a “smooth ceiling” is defined as a continuous ceiling free from significant irregularities, lumps, or indentations. (NFPA 13, 2007 Edition, 3.3.4.) Underwriters' Laboratories® Standard 1626 covers generally fire protection standards for smooth flat horizontal ceilings for residential occupancies, and UL Standard 1626a (May 22, 2007) covers fire protection standards for sloped ceilings having a pitch not exceeding 8/12. The requirements of UL 1626a cover the fire testing of residential sprinklers for use with smooth, sloped ceilings having pitches not exceeding 8/12 for installation in accordance with the Standards for Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, NFPA 13D; Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height, NFPA 13R; and Installation of Sprinklers, NFPA 13.
As used in the remainder of this specification, the term “sloped ceiling” includes all ceilings having a non-zero pitch, which includes horizontal and sloped ceilings as those are defined in NFPA 13.
Rooms having sloped ceilings present specific challenges not found with rooms having smooth flat ceilings with substantially zero pitch. One difference between the two occupancies is that for two rooms having the same floor area and sharing at least one common wall height, the room with the sloped ceiling has a larger volume and an increased floor-to-sprinkler distance. These factors, taken together, tend to increase the response time for sprinklers in a room with a sloped ceiling when compared to those sprinklers used in a smooth, flat, zero-pitch ceiling sprinkler configuration. As a result of such delay in sprinkler activation, the fire has a longer period to burn and spread before activation, and so requiring a larger amount of water to control the heat release than for a flat horizontal ceiling.
A number of design factors affect the fluid flow to sprinklers installed for sloped ceilings. For example the piping sizes of the fluid supply conduit can be increased, the pressure of the fluid supply entering the sprinklers can be increased, and the orifice of the sprinkler (indirectly designated by the discharge coefficient, commonly known as the “K-factor”) can be increased. The K-factor is a sprinkler's constant at a given volume flow rate and is generally calculated according to the relation: K=Q/√p, where Q is the volumetric flow rate (gpm), and p is the pressure of the fluid at the inlet of the sprinkler (psi). Modifying the fluid supply system to meet the increased fluid demand described above is costly and undesirable. It is therefore desirable to be able to provide a sloped ceiling fire protection system that does not substantially increase the cost as compared to a system that protects a similar room with a horizontal flat ceiling.